FIGS. 1 and 2 show the human eye 50 in section. The cornea 52, the iris 54 and the natural crystalline lens 56, which is situated within the elastic, membranous capsular bag or lens capsule 58, are specifically illustrated for a more thorough understanding of the invention. The capsular bag 58 is surrounded by and suspended within the ciliary muscle 60 by ligament-like structures called zonules 62.
As light enters the eye 50, the cornea 52 and the lens 56 cooperate to focus the incoming light and form an image on the retina 64 at the rear of the eye to facilitate vision. During the process known as accommodation, the shape of the lens 56 is altered (and its refractive properties thereby adjusted) to allow the eye 50 to focus on objects at varying distances. A typical healthy eye has sufficient accommodation to enable focused vision of objects ranging in distance from infinity (generally defined as over 20 feet from the eye) to very near (closer than 10 inches).
The crystalline lens 56 has a natural elasticity, and in its relaxed state assumes a shape that in cross-section resembles that of a football. Accommodation occurs when the ciliary muscle 60 moves the lens from its relaxed or “unaccommodated” state (shown in FIG. 1) to a contracted or “accommodated” state (shown in FIG. 2). Movement of the ciliary muscle 60 to the relaxed/unaccommodated state increases tension in the zonules 62 and capsular bag 58, which in turn causes the lens 56 to take on a thinner (as measured along the optical axis) or taller shape as shown in FIG. 1. In contrast, when the ciliary muscle 60 is in the contracted/accommodated state, tension in the zonules 62 and capsular bag 58 is decreased and the lens 56 takes on the fatter or shorter shape as shown in FIG. 2. When the ciliary muscles 60 contract and the capsular bag 58 and zonules 62 slacken, some degree of tension is maintained in the capsular bag 58 and zonules 62.
In response to various physiological conditions, the most notable being the occurrence of cataracts, the natural crystalline lens may have to be removed. It is often replaced by an intraocular lens (IOL). Since the natural lens accounts for the eye's ability to accommodate, as described above, the implantation of an accommodating IOL is intended to re-establish this ability (to a lesser or greater degree) and eliminate the need for additional lenses such as spectacles, for example, for focusing near-vision objects. Accommodating IOLs typically consist of a single optical element, but multi-component (two or more optical elements) accommodating IOLs are in development. A two-element accommodating IOL, for example, will generally provide more focusing power and accommodative range than a single-element accommodating IOL. Embodiments of the current invention are advantageously directed to a two-element accommodating intraocular lens referred to herein as the A-IOL.
The accommodative operation of the A-IOL is similar to that described above for the natural crystalline lens. The A-IOL replaces the natural lens and thus is disposed within the evacuated capsular bag. The A-IOL includes an anterior (front or closer to the cornea) optic and a posterior (back or closer to the retina) optic. Depending upon the particular design of the A-IOL, the anterior and posterior optics are connected by a biasing structure that generally serves three primary functions: i) biasing the position of one optic relative to the other in a natural, most-spaced-apart, accommodating state of the A-IOL; ii) allowing the anterior optic to translate axially relative to the posterior optic in response to a force exerted by the ciliary muscle and zonules acting on the capsular bag; and iii) fitting/securing the A-IOL in the capsular bag so that it remains aligned and able to function properly in the eye over an extended period of time. This biasing structure is referred to as a haptic (one or more), a bridge, a connector, and other terms widely recognized in the art. As described in greater detail below, the biasing structure according to embodiments of the present invention include one or more deformation features that allow the biasing structure to be compressed. According to the embodiments of the invention disclosed and claimed herein, this biasing structure will be referred to as a ‘compressible haptic’.
With respect to multi-component A-IOLs, one view in the field is that the biasing structure should consistently conform to the inner dimensions (shape and size) of the capsular bag and be able to slide rather than stick to the interior of the bag. A non-conforming or sticky lens fit, for example, may adversely impact lens performance, ocular physiology and wearer comfort. Another concern with the design and development of A-IOLs is their ability to conform to capsular bags of a diameter smaller than they are intended to be compatible with. However, capsular bag dimensions are known to vary among the IOL-receiving population. Currently, capsular bag dimensions in live subjects are not accurately measurable. In addition, it is known that the capsular bag shrinks post-operatively after natural lens removal and bag evacuation. These conditions are believed by some to have negative effects on the ability of known A-IOL lens designs to maintain their shape in the eye and deliver the requisite performance.
Accordingly, the inventor has recognized a need for improvements in design and construction of multi-component accommodating IOLs to account for population variation in capsular bag dimensions and/or post-operative bag shrinkage. Embodiments of the invention described herein below will describe such improvements and illustrate the benefits associated therewith.